An information recording medium on which information can be recorded by means of a laser beam is known as a recordable compact disc (CD-R), and is widely used, for instance, as a large capacity computer data disc.
The optical disc of CD-R type generally comprises a disc-shaped substrate (support) made of polymer and a recording layer provided thereon on which information can be recorded by means of a laser beam. The recording layer comprises a metal such as In or Te, or alternatively a dye such as a cyanine dye.
The recording layer comprising dye can be easily formed by a coating method and shows a high sensitivity, as compared with the recording metal layer. The such recording dye layer is very advantageous in view of production costs, but the dye layer has such disadvantages as low light-resistance and low heat resistance. Therefore, it has been desired to develop a recording dye layer having high durability against light and heat, as well as high recording and reproducing characteristics.
In order to improve the light-resistance of recording dye layer, various compounds known as singlet oxygen quenchers are generally added to the recording dye layer. For example, a transition metal chelate complex is contained as singlet oxygen quencher with a cyanine dye in the recording layer of the information recording medium disclosed in Japanese Patent Publication No. H1-38680 and Japanese Patent Provisional Publication No. H4-146189. In Japanese Patent Provisional Publication No. H2-300288, a nitroso compound is used as a singlet oxygen quencher for a cyanine dye. Further, Japanese Patent Provisional Publication No. 63-209995 describes an optical disc having a recording layer which contains an oxonol dye and a transition metal complex of singlet oxygen quencher. According to the publication, such optical disc shows stable recording and reproducing characteristics for a long period of time.
However, most of the above transition metal complexes are environmentally unfavorable compounds. Further, when the nitroso compound is used as the singlet oxygen quencher, a considerable amount of the compound must be added so as to sufficiently enhance the light-resistance, but the increased amount of the compound often lowers the light-reflection of the optical disc. Since an optical disc is required to have a high light-reflection, the incorporation of the increased amount of the nitroso compounds is not advantageous.
U.S. Pat. No. 4,656,121 discloses an optical disc having a recording layer which comprises a diimmonium compound and a dye such as a cyanine dye or a merocyanine dye. However, since the diimmonium compound also absorbs the light of laser, the reflection of the laser beam is apt to lower in the case that an increased amount of the diimmonium compound is used.
Accordingly, it is an object of the present invention to provide a method for preventing an organic dye from fading, so that the light-resistance of the recording dye layer can be improved.
It is another object of the invention to provide an information recording medium having recording characteristics and particularly high light-resistance to show satisfying recording characteristics for a long period.